1. Field of the Invention
This invention relates generally to metathesis and hydrogenation chemistry. More particularly, it relates to a method of completing these two types of chemical reactions without the need for isolating/purifying the intermediate product.
2. Background of the Art
Metathesis chemistry has received much attention recently as a means to obtain precise structure control in polymer synthesis. Recent advances include the synthesis of polyolefin and polyolefin-like polymers through two-step procedures involving (1) acyclic diene metathesis (ADMET) polymerization or ring-opening metathesis polymerization (ROMP) followed by (2) hydrogenation. Examples of such polymerizations include perfectly linear polyethylene (O'Gara, J. E., et al., die Makromomolekulare Chemie 14:657, 1993; Grubbs, R. H. and W. Zhe, Macromolecules 27:6700, 1994), telechelic polyethylene (Hillmyer, M. A., "The Preparation of Functionalized Polymers by Ring-Opening Metathesis Polymerization", Ph.D. Dissertation, California Institute of Technology, 1995), ethylene/vinyl alcohol copolymers (Valenti, D. J. and K. B. Wagener, Macromolecules 31:2764, 1998) and polyethylene with precisely spaced alkyl side chains (Valenti, D. J. and K. B. Wagener, Macromolecules, 30:6688, 1997). The disclosure of the above publications, and of all the other articles, publications, and patents cited hereafter, are incorporated by reference as if fully set forth herein.
FIG. 1 shows some examples of metathesis reactions. L.sub.n M=-R represents any metathesis catalysts (which are well known in the art) where L.sub.n represents a ligand set, M represents a transition metal, and -R represents a hydrocarbon group. Further, R and R' represent any functionality which does not deactivate the metathesis catalyst. All of these metathesis reactions are useful means for constructing molecules. It may however be desirable that the products be free of carbon--carbon multiple bonds. Conversion of these multiple bonds to single bonds (hydrogenation) can significantly influence physical and chemical properties, biological activity, oxidative stability, etc. Substrates may contain a wide group of functionality. The possible scope of application of this methodology is vast. A few possible applications follow.
The overall result of this process is the formation of carbon--carbon single bonds. This is highly useful in organic synthesis. Unsaturated vegetable oils may be functionalized by cross-metathesis with functionalized olefins and then hydrogenated. Cyclic molecules may be constructed and then hydrogenated. Difunctional monomers with long aliphatic chains, which may otherwise be difficult to product, may easily be synthesized. U.S. Pat. No. 4,496,758 describes metathesis and cross-metathesis of alkenyl esters to produce unsaturated monomers which can be used in polymer synthesis, sex pheromones, etc. U.S. Pat. No. 5,146,017 describes metathesis of partially fluorinated alkenes and states that if the products were to be hydrogenated they would produce highly heat resistant specialty lubricants.
Metathesis chemistry has been shown to be effective in the synthesis of a broad range of polymers. A common feature of all polymers produced via metathesis is unsaturation in the main chain. Oxidative stability can be increased by removal of this unsaturation. Therefore, polymers which may be difficult to synthesize (or even completely inaccessible) by other means may be produced by metathesis and then value added by saturating the double bonds. Other properties may be manipulated such as toughness, thermal stability, permeability, crystallinity, etc.
Currently, metathesis polymers are typically prepared, isolated, and purified prior to hydrogenation. Additional hydrogenating agents are then added and hydrogenation is effected. Disadvantages are loss of product during isolation and purification after the first step, the added effort to conduct reactions in additional vessels, use of additional reagents to effect hydrogenation, and the isolation and purification of the polymer from reagents used in the hydrogenation.
These syntheses typically involve first the synthesis and isolation of unsaturated polymers followed by a second hydrogenation step. Two of the more successful methods for hydrogenation are diimide reduction (Valenti, D. J. and K. B. Wagener, supra, 1997) and catalytic hydrogenation with Crabtree's iridium complex (Hillmyer, M. A., supra, 1995). The Valenti method requires an excess of the hydrogenating species and the Hillmyer method attains complete hydrogenation only if the olefin/catalyst ratio was kept less than or equal to 100:1.
Recently, McLain, et al. (McLain, S. J., et al., Proceedings PMSE 76:246, 1997) reported a one-pot procedure for producing ethylene/methyl acrylate copolymers by the ROMP of ester-functionalized cycloolefins using Cl.sub.2 (PCy.sub.3).sub.2 Ru.dbd.CHCH.dbd.CPh.sub.2 and then hydrogenating by simply applying hydrogen pressure to the completed ROMP reaction system. The metathesis catalyst residue was assumed to be converted to RuHCl(PCy.sub.3).sub.2 in the presence of hydrogen gas. RuHCl(PCy.sub.3).sub.2 is an effective hydrogenation catalyst. However, hydrogen pressures of at least 400 psi were required to maintain catalytic activity and achieve greater than 99% reduction.
U.S. Pat. No. 5,539,060 describes the one-pot ROMP of cyclic olefins and subsequent hydrogenation without the need for isolation of the polymer from the first step or deactivation of the olefin metathesis catalyst. However, metathesis is effected with a binary catalyst system (e.g. WCl.sub.6 /SnBut.sub.4) and then another catalyst must be added for hydrogenation. Further, in some cases hydrogen halides can be produced in this process. An acid binder is required in these cases as such by-products can cause corrosion in reaction vessels.
It would be advantageous if olefin metathesis and the subsequent catalytic hydrogenation could be conducted in a single vessel where the only added reagents are low cost support materials and hydrogen gas. It would also be advantageous if quantitative hydrogenation could be achieved under mild conditions (e.g., low to moderate hydrogen pressures and temperatures) and if purification of the final product could be achieved by simple filtration and solvent removal (if used) with minimal loss of product. We have now discovered such a method which surprisingly offers the above advantages and which result in the increased cost efficiency for olefin metathesis and the subsequent catalytic hydrogenation of the metathesis product.